Receiver for radio positioning signals

ABSTRACT

A GPS or Galileo receiver for radio positioning signals wherein at least a part of the computing of position related data based on radio signals received from a plurality of space vehicles is carried out by a processor ( 21 ) mounted on a graphic or sound card ( 20 ). The receiver thus makes use of available computing resources, thus achieving a lower Bill of Material.

This utility patent application is a continuation of internationalpatent application PCT/EP2006/063346, filed Jun. 20, 2006, the contentof which is incorporated by reference.

TECHNICAL DOMAIN

The present invention relates to a receiver for radio positioningsignals, in particular to a receiver for the acquisition and tracking ofsatellite localization signals such as GNSS (Global Navigation SatelliteSystem), GPS, GLONASS or Galileo signals. The present invention alsorelates to software used in such a receiver.

DESCRIPTION OF RELATED ART

FIG. 1 illustrates an example of a known software GPS receiver. Theillustrated receiver comprises a first chip 1 to do the RF-downconversion and digitization, and a second module 2, usually built arounda general purpose processor or a digital signal processor 9, that runs aprogram for performing the correlation and tracking procedure as well asthe navigation. Both chips are mutually connected over a proprietarydata bus 3. Solutions including both modules in a single chip have alsobeen suggested.

In a GNSS system the sources are orbiting GNSS Space Vehicles (SV). Inthe case of the GPS, which is readily extendable to otherradiolocalization systems, each space vehicle transmits two microwavecarrier signals. The signal L1 at 1575.42 MHz carries the navigationmessage. The signal L2 at 1227.60 MHz is used among others to measurethe ionospheric delay. The L1 and/or L2 signals are modulated with threebinary codes:

-   -   The C/A Code (Coarse Acquisition) modulates the phase of the L1        carrier signal. The C/A code is a Pseudo Random Noise (PNR) at 1        MHz that repeats every 1023 bits (1 millisecond). Each SV uses a        different C/A code. This noise-like code spreads the spectrum of        the modulated signal over a 1 MHz bandwidth to improve immunity        against noise.    -   The navigation message also modulates the L1-C/A code signal. It        is a 50 Hz signal consisting of data bits that describe the GPS        satellite orbits, clock corrections and other system parameters.    -   The P-Code (precise) modulates both the L1 and the L2 signals,        and is for use only by authorized users with cryptographic keys.

The task of a GPS receiver is to retrieve the signals received from thevarious space vehicles that can be seen at a given instant. For that,the circuit of FIG. 1 comprises an antenna 4 whose output signal isamplified in the first chip 1 by a low-noise amplifier 5 anddown-converted to an intermediate frequency signal (IF signal) in theconversion unit 6, before being fed to the carrier removal stage 7. TheIF signal often comprises one in-phase (i) and one quadrature (q)component, which are converted by analog to digital converter 8 intodigital signals (I, Q) delivered over a data bus 3 to the second module(“correlator”) for further processing.

The function of the correlator 2 is mainly to de-spread the signals I, Qdelivered by the RF chip and originating from the various SVs. For that,the correlator aligns temporally the incoming signals with locallygenerated copies of the PNR signals of each existing or likely SV. Inorder to reduce the computation overhead and the acquisition time,alignment is often performed in the frequency domain, by correlating aFFT transform of the incoming signals I, Q with FFT transforms of thePNR signals characterizing each SV. There are various algorithms used bydifferent manufacturers for carrying out this correlation in the time orfrequency domain. It is however due to the fact that the correlation andde-spreading processes tend to require a lot of processing power. Forexample, a correlation in the frequency domain requires a lot ofprocessing power for the computation of FFTs, multiplication by thecomplex conjugates of the CA Codes, and Inverse FFT on the results thatare needed for a fast time-to-frequency conversion.

In addition to the processing requirements this process also requires alarge amount of storage for data and results.

The correlator 2 outputs digital processed data that are fed over thedata bus 3 to an acquisition and navigation processor 11 for computingand for displaying position related data, including for example theposition of the receiver. The nature of the data output by thecorrelator depends on the receiver; some modules already deliver thelocation coordinates while others only deliver intermediary values suchas Pseudo Ranges of the orbiting SV's.

In the prior art, the correlator 2 is often built around a generalpurpose or digital signal purpose processor 9 accessing its own data andinstruction memory 10. Examples of known correlators include the NJ1030and NJ2020 baseband processors produced by the applicant.

It is also known to use an FPGA or a dedicated ASIC as a correlator forcomputing the FFTs and for the various other computations performed bythe module 2.

Processors, Asics and FPGA are however expensive, power and spaceconsuming, therefore, the hardware resources 2 required for thecorrelation and tracking procedures have a significant impact on theprice, volume and power-consumption of the overall receiver.Additionally these resources are often dedicated to the GPS algorithmand cannot be used for other purposes even when they are no longerrequired by the GPS function.

It has also been suggested to use a general purpose CPU 11 in the systemfor the computation of the FFT required for the correlation. Althoughgeneral purpose CPUs are fast, the total system throughput is often notfast enough. Moreover, this solution makes an inefficient use of theavailable memory bandwidth and puts a high load on the CPU, thus,blocking it from other tasks.

It is therefore a goal of the present invention to provide the digitalprocessing power required by a radio positioning signal receiver in aless expensive, less power-consuming and less space consuming way thanin the prior art, and in a manner which shares the resources efficientlyso that they can also be used for other system functions when notrequired by the navigation functions.

BRIEF SUMMARY OF THE INVENTION

According to the invention, these aims are achieved by means of theobject of the independent claims. Further optional features are theobject of the dependent claims.

In particular, these aims are achieved by means of a receiver for radiopositioning signals comprising digital signal processing parts as partof a graphic or sound card for the computing of position related databased on radio signals received from a plurality of space vehicles.

In the context of this application, “position related data” is notlimited to the position itself, but also encompass any data derived fromthe position, including the speed, acceleration, altitude, etc, as wellas any intermediate data or values used for computation of the positionfrom the radio positioning signals received by the receiver. Theposition related data includes for example the FFT transforms of signalsderived from the received signals, or properties, for example code andDoppler shifts, of candidate correlation peaks, computed by the card,even if a single FFT value or a set of correlation peaks do not yetallow a full determination of the pseudo ranges or position.

These aims are also achieved by a receiver for radio positioning signalscomprising:

a high frequency part for the acquisition and processing of analog radiosignals from a plurality of satellites, said high frequency partdelivering digital intermediary signals,

digital signal processing parts for the de-spreading of said digitalintermediary signals,

wherein said digital processing parts comprises a processor as part of agraphic or sound card.

Graphic processing units are usually significantly faster than generalpurpose CPUs, but they are specialized for specific task, especiallyrepetitive tasks requiring a large memory bandwidth. Much of theavailable processing power offered by graphic cards is used only by fewapplications, like games and graphic software, and remains unused duringother applications, like office and geographic navigation programs.Therefore, according to the invention, the computing-requiring tasks ofGPS computations are performed by the graphic or sound card that remainsfor the most part unused during many GPS-based applications.

Additionally, in 3D Graphics and Audio applications these processors areusually attached to large dedicated memories with high bandwidthcapabilities used typically for storing and processing textures andaudio images. In all but the most demanding games applications these aregenerally mostly unused and can be re-targeted for use in GPS functions.

In most 3D audio and Graphics applications the associated processors areoptimized for performing repetitive mathematical tasks on blocks of dataand are ideally suited for efficiently performing the functions requiredfor the GPS signal processing.

The receiver thus takes advantage of the available resources in thesystem more efficiently than the traditional approach.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with the aid of the descriptionof an embodiment given by way of example and illustrated by the Figureswherein:

FIG. 1 is a block diagram illustrating a known software GPS receiver.

FIG. 2 is a block diagram illustrating a first embodiment of receiveraccording to the invention.

FIG. 3 is a block diagram illustrating a first embodiment of receiveraccording to the invention.

FIG. 2 illustrates an embodiment of a receiver for radio positioningsignals according to the invention. This receiver may be used forreceiving and processing signals from GPS, Galileo or Glonasssatellites, or from terrestrial positioning systems. It is built arounda general purpose computer, such as a personal computer, a laptop, apalmtop, a portable media player, an Origami computer, a smartphone,etc. The receiver therefore generally comprises one or more generalpurpose processors 11, for example a Pentium, ARM, or ARC processor, forrunning an operating system and software applications, includingnavigation software and other office utility, communication and gameapplications. Other components, including a general purpose RAM, inputand output peripherals such as display, loudspeaker, keyboard, pointingdevice, drives, etc, are globally referred with reference number 12 andconnected to the processor over a general-purpose bus, such as a PCI,AMBA, or preferably PCI-Express bus, or through other non illustratedcomponents. The receiver also includes communication interfaces 13(WLAN, Bluetooth, cellular, Ethernet, etc,) for communicating withexternal systems 14, possibly including positioning assistance servers.

A graphic and/or sound card 20 provides computing functions required forvisual and/or audio restitution of data. The graphic/sound card 20 isbuilt around at least one processor 21, for example a digital signalprocessor or a dedicated graphic or sound processor, and accesses itsown data memory 22 and instruction memory 23. Frequently thegraphic/sound card includes one or several groups of parallelprocessors, designed to perform several tasks of similar nature at thesame time. The general architecture of the receiver may be conventionaland does not need to be described with more details.

The receiver of the invention also comprises a high frequency part 1,preferably mounted on a removable card inserted in a slot of thereceiver, for example a PCI-Express card. The high frequency part may,for example, comprise analogue components and build a super-heterodynereceiver front-end for receiving signals in the GPS L1 band. It includesa connector for an external GPS antenna 4. Signal from the antenna isfed to a low noise amplifier 5, for example, a single stage cascadedevice. The signal is then fed to a conversion unit 6, for example, asingle-balanced mixer that converts the radio-frequency signal to thebaseband or preferably to an intermediate frequency. Filter means 7 areprovided at the output of the conversion unit 6 to remove the carrierand to select the desired signal bandwidth. Analog-to-digital converters8 converts the analog signals at the output of the stage 7 into twoseries of words, encoding into two orthogonal digital signals I and Qdelivered over the data bus 3 to the second module (“correlator”) forfurther processing.

In an embodiment, the RF module 1 may be built around a conventionalNJ1006A or compatible chip.

According to a variant of the invention not represented in the pictures,the high frequency part 1 does not provide directly digital demodulatedsignal I and Q, but rather a signal in which the signals I and Q aremodulated over a low frequency intermediate carrier (low IF). In thesubsequent stages of the receiver, the low IF signal is converted into Iand Q baseband signals by known means.

According to the invention, at least one part of the instruction memory23 of the graphics or sound card 20 has been programmed so as to includefunctions for computing position related data, or intermediate valuesfor the determination of the position, based on data delivered by the RFmodule 1. In an embodiment, the instruction memory 23 of the card 20 isa permanent or semi-permanent memory, such as an EEPROM for example,that has been programmed during manufacture or personalization toinclude software code for computation of the functions and methodsrequested by the location signals receiver. In another embodiment, theprocessor 21 of the card 20 is able to run software code stored in theinstruction memory 23 or in the system 12 and that can be dynamicallyupdated at any time. In both situations, the processor 21 of the card 20responds to instructions 210 received over the bus 30 for deciding onthe portion of software code to execute at each moment.

Computation of the position related data by the card 20 is preferablydone in parallel to the execution of other functions of the card. Inthis case, display by the graphic card may be slowed down duringcomputation of position related data, and/or the use of some extendedgraphic or sound functions may be momentarily prevented. In anotherembodiment, the card is entirely devoted to the computation of thepositioning data during use, and the display, or at least one part ofthe display, is temporarily frozen during the acquisition and/ortracking process.

The functions performed by the processing means 21 on the card 20 mayinclude some or all of the functions performed by the correlator 2 inthe prior art embodiment of FIG. 1. More specifically, the processor 21can run any function needed for the acquisition and/or tracking ofsignals from the various space vehicles, including correlation functionsfor temporal alignment, in the time or frequency domain, of the signalsdelivered by the RF part 1 with locally generated copies of the PRNsignals of each existing or likely space vehicle. The graphic or soundcard may thus include and execute routines for generating those copiesof the PNRs signals, and/or routines for performing the correlation ofsignals.

According to a preferred embodiment of the invention, the correlation ofthe signals delivered by the RF part 1 is carried out by a correlationengine in the frequency domain, implemented by appropriate softwareelements executed by the processor 21 of the card 20 and, preferably,stored in a memory 23 of the card 20. In this case the processor 21 ofthe card 20 is programmed, for example, with routines for computingFourier transforms, for example FFTs and inverse FFTs, etc.

The correlation operation being equivalent to a simple multiplication inthe frequency domain, the processor 21 will be preferably programmed tocompute, or retrieve from a pre-calculated table, the Fouriercounterparts of the PRN signals of each existing or expected spacevehicle, and evaluate the corresponding correlation function with theincoming RF signal from the RF front-end. The person skilled in the artwill appreciate that this frequency domain approach is especiallyappropriate when the received signals are weak and, consequently, thesearch space is very large.

The large computational bandwidth of the processor 21 allows, in thiscase, to acquire and track weak GPS signals with high-sensitivity,without placing a large burden on the main processor 11.

Preferably the correlation data computed in the card 20 used to obtainthe relative time shifts of pseudorandom noise codes comprised in thesignals delivered by said high frequency part 1, and received from thedifferent satellites in sight. Such relative time shifts are indicated,for example, by the position of the correlation peaks for thecorresponding satellites in histograms accumulated in the card 20.

Preferably, the correlation data computed in the card 20 aretransferred, by means of the bus 30, to a navigation module implementedby appropriate software modules, executed by the main processor 11. Oncea sufficient number satellite signals are detected and tracked, thecorrelation module uses the determined relative shifts, indicated forexample by the position of the corresponding correlation peaks, todetermine the position of the receiver, as it is known in the art. Theinvention includes, however, also variants in which parts or all of thefunctions of the navigation module are delegated to the processor 21 ofthe card 20.

In the case of an assisted GPS system, the functions executed by thegraphic card may also use assistance information retrieved from externalassistance servers 14 by the main processor 11 and transmitted to thegraphic card over the bus 30.

In a preferred embodiment, the functions of the graphic card 11 arepiloted by a suitable program run by the general purpose processor 11 ofthe system. The processor 11 also runs the operating system andapplication software, including a navigation software for computing theposition and other data based on digital data computed and output by thecard 20. As already mentioned, the system may also comprise one orseveral communication interfaces 13, for example a cellular, WLAN,Bluetooth or Ethernet connection for accessing external devices 14 andretrieving assistance data to help the receiver for a fast acquisitionof position, even in difficult condition such as indoors or in urbancanyons, as well as maps or traffic information for example.

In the embodiment of FIG. 2, all computations in the baseband areperformed by the sound or graphic card and by the general purposecomputer 11. The only additional components that are added to a GPS-lesssystem are the antenna 4, the RF-chip 1 and possibly a memory 23 on thegraphic card 20 with an additional set of instructions. The cost andcomplexity of the system are thus very low, but the computing load onthe graphic card and on the general purpose processor 11 is high.

FIG. 3 illustrates another embodiment of the invention in which anadditional baseband digital component 21 is provided, preferably on theextension card 1, for performing a part of the computing operations inthe baseband and/or intermediary frequency band. The additionalcomponent 21 may be built as an independent chip or set of chips, or asa digital module on the RF chip 1. This additional component carries outa part of the operations performed by the graphic card 20 and/or by themain processor 11 in the embodiment of FIG. 2, and thus reduces the loadand requirements for those components. Sharing of the computingoperations between the component 21, the graphic card 20 and the mainprocessor depends on the implementation, but in a preferred embodimentthe component 21 will perform all tracking and acquisition computations,whereas repetitive tasks such as computation of FFTs is delegated to thegraphic card 20. The main processor 11 is then responsible to carry outthe user's front end application, including the user interface and thedisplay of results. The baseband digital component 21 may also directlycommand the processor 21 of the graphic or sound card 2 and make itperform computations needed by the tracking or acquisition algorithms.

It is also possible to duplicate functions and to provide the samefunctionalities in the processing system of the graphic card and in theadditional component 21 and/or in the general computing system 11. Thechoice of one or the other module to perform one operation at a specificmoment depends then for example on the current load and availability ofeach component, on the required speed and/or on the power consumption.For example, the system may decide to compute FFT with the graphic card20 at a particular moment, in order to put the additional component 21or some parts of this component in stand-by mode and reduce the powerconsumption, and to use the additional component and/or the generalpurpose computer at a different moment when a fast acquisition isrequired.

Since during acquisition the time and frequency uncertainties aregreater the computation in the frequency domain is an efficient approachto improve acquisition sensitivity and speed, however once SV's areacquired processing in the time domain can be more energy efficient,another embodiment of the system uses the graphics/sound card toaccelerate acquisition and/or re-acquisition and then transfers thenecessary information to a dedicated correlation engine operating in thetime domain for efficient and low power tracking, thus relieving theburden on the graphics/sound card after the initial few seconds requiredfor the acquisition.

1. A receiver for radio positioning signals comprising digital signal processing parts for the computing of position related data based on radio signals received from a plurality of space vehicles, characterized in that said digital processing parts comprises computing means, for example a processor, as part of a graphic or sound unit on a card.
 2. The receiver of claim 1, further comprising a high frequency part for the acquisition and processing of analog radio signals from a plurality of space vehicles, said high frequency part delivering digital intermediary signals (I, Q), or an intermediate IF data signal.
 3. The receiver of claim 1, wherein said computing of position related data performed by said graphic or sound unit comprises the de-spreading of said digital intermediary signals so as to deliver a plurality of digital signals corresponding to a plurality of emitters of said radio positioning signals.
 4. The receiver of claim 1, wherein said computing of position related data performed by said graphic or sound unit comprises the computation of FFTs.
 5. The receiver of claim 1, wherein said computing of position related data performed by said graphic or sound unit comprises determination of relative time shifts of pseudo random noise codes comprised in the signals delivered by said high frequency part.
 6. The receiver of claim 1, further comprising data restitution means for the visual and/or audio restitution of position related data based on data output by said digital signal processing parts.
 7. The receiver of claim 6, said data restitution means comprising a graphic or sound card for the visual or audio restitution of graphic or audio data, wherein said processor used by said digital processing parts is part of said graphic or sound card.
 8. The receiver of claim 1, said graphic or sound unit comprising a data memory, an instruction memory and a graphic or sound processor, said instruction memory comprising first instructions for the processing of graphic or audio data for restitution by said data restitution means, and second instructions for the processing of said position related data by said graphic or sound processor.
 9. The receiver of claim 2, said digital intermediary signals delivered by the high frequency part comprising at least two orthogonal signals (I, Q).
 10. The receiver of claim 2, said high frequency part being mounted on a card and comprising: an antenna connector for connection of an antenna, amplifiers for amplifying input signals from said antenna, analog signal filtering means, baseband conversion means for demodulating input signals, analogue to digital converting means for converting analog demodulated signals into said digital intermediary signals.
 11. The receiver claim 2, said high frequency part being connected to said graphic or sound card over a general purpose computer bus, for example a PCI or Express-PCI bus.
 12. The receiver of claim 2, said high frequency part being connected to said graphic or sound card over a dedicated bus.
 13. The receiver of claim 6, said data restitution means comprising one or more processors for running a navigation program.
 14. The receiver of claim 2, being made up of a personal computer, laptop or palmtop including said graphic card and a card including said high frequency part.
 15. A method for the computing of position related data based on radio signals received from a plurality of space vehicles, characterized by computing steps carried out by a graphic or sound unit on a card.
 16. The method of claim 15, wherein said computing steps comprises the de-spreading of digital intermediary signals (I, Q) or IF delivered by a high frequency part.
 17. The method of claim 15, wherein said computing steps comprise the computation of Fourier transforms, for example FFTs and/or inverse FFTs.
 18. The method of claim 15, wherein a decision to have said steps carried out by said graphic or sound unit is automatically taken depending on power consumption criteria.
 19. The method of claim 15, wherein a decision to have said steps carried out by said graphic or sound unit is automatically taken depending on the current load of components of a receiver.
 20. The method of claim 15, wherein a decision to have said steps carried out by said graphic or sound unit is automatically taken depending on a requested acquisition speed and/or sensitivity.
 21. A graphic card comprising a graphic processor and a memory with instructions for the computing of graphic functions, characterized in that memory further comprises instructions for the computing of position related data based on radio signals received from a plurality of space vehicles.
 22. A method of providing a receiver for radio positioning signals comprising the steps of providing digital signal processing parts for the computing of position related data based on radio signals received from a plurality of space vehicles, characterized in that said digital processing parts comprise a processor as part of a graphic or sound unit on a card. 